Unique human penis

The inside of the penis consists of three long rod-like tissues, often called as sponge. Which consists of two strips of cylindrical tissue, filled with gaps, both side from the top of the penis extension to the root place, and the third one is the sponge body, mainly in the bottom of the penis. They are soft under the normal, like a discouraged balloon, but in the penis erection, all the gap will be full of blood. When with sexual desire, the injected amount of blood even be 8 times than the normal state, and these blood completely flowed into the penis.

These three stretchable tissues are tightly surrounded by fibers commonly called connective tissue. In order for the erect penis to straighten out, this layer must be able to withstand its dilation without rupture, or the direction of the erection will change once it breaks. Although the rupture is rare, if it does rupture, it needs repaired by surgery.

There is one thing is very intriguing, that only human penis do not contain any bones among all primates. In mammals, including rodents, hedgehogs, whale, and bats, almost all animals have penis bone, which provide the support for erection.

The urethra is distributed along the direction of the penis, which holds both urine and semen. To prevent urination and ejaculation happen at the same time, the body has a flap structure that closes the bladder neck during ejaculation, which is very smart design.

The tip of the penis, which is always called as penis glans that is the most sensitive part of the penis because it is tightly distributed with a large number of nerve endings. When a boy is born, the glans is covered with a thin layer of skin, usually referred to as penis foreskin, while the foreskin inside the epidermis contains the secretion of sebum material glans. The function of this layer of foreskin is to reduce the friction of the penis when it swells and shrinks.